Create a function that takes a string of words and returns the highest scoring word. Each letter of a word scores points according to it's position in the alphabet: a = 1, b = 2, c = 3, etc.
wordRank("The quick brown fox.") ➞ "brown"
wordRank("Nancy is very pretty.") ➞ "pretty"
wordRank("Check back tomorrow, man!") ➞ "tomorrow"
wordRank("Wednesday is hump day.") ➞ "Wednesday"